1. Field of the Invention
This invention relates to cooling systems, more particularly to cooling system for cooling electronic components.
2. Description of the Related Art
Many cooling systems for electronic components, such as those systems used to cool electronic components in missiles, have proven to be inadequate due to the extremely high temperatures which the electronic components are exposed. With a missile, the skin or surface of the missile can reach extremely high temperatures during flight, in some cases exceeding 1000.degree. F. Packaged within the missile cylinder are electronic components which must operate prior to and during the launch and flight phase of the missile. The temperature of an electronic component prior to launch is estimated to be as high as 85.degree. C. (185.degree. F.). This temperature build-up prior to launch can be caused by many factors, such as the outside ambient temperature and the heat generated by the component itself or by other components in the missile. Also, during carriage-flight ( that is, when a missile is being carried by an aircraft prior to launch from the aircraft) heat is built-up from the air friction. Whatever the source, the increase in temperature is a severe problem because the maximum junction temperature for a typical electronic component after launch should not exceed 100.degree. C. to 110.degree. C. Therefore, with an estimated prior-launch electronic component temperature of 85.degree. C. only a 15.degree. C. to 25.degree. C. rise in temperature is allowed during the flight period.
Another problem that is particularly important with missile systems and other flying devices is that the electronic component cooling system should be as light weight and compact as possible. Bulky, heavy cooling systems that use large reservoirs, heat pipes, motors or condensers may not be acceptable.
Methods to keep the electronic components cool include the use of insulation to keep the skin heat from entering the interior and system mass storage. Such methods include the use of aluminum in the missile assemblies. Unfortunately, capacitance or mass x specific heat from metal is inefficient for heat storage and results in a weight penalty which affects the flight performance of the missile.
To a somewhat lesser degree, phase change material which melts at a prescribed temperature can be made to absorb the heat, but this method is also inefficient and has poor heat conductivity.
Other cooling systems tend to be closed systems where a phase change material is "recycled" from phase to phase, such as with a heat pipe. These systems tend to be relatively heavy.